Electrical transformer construction

In this post, we will discuss electrical transformer construction.

Electrical transformer construction:

An electrical transformer mainly consists of the followings-

Electric circuit

Dielectric circuit

Magnetic circuit

Tanks and accessories

The electrical transformer construction is quite simple it consists of two magnetically linked windings, wound on two separate limbs of iron. It consists of the following basic parts:

Two inductive windings (Primary winding & Secondary winding)

Laminated steel core

The coils are insulated from each other as well as from the steel core.

Electric circuit

The electric circuit of the transformer consists of primary and secondary windings. These windings are usually made of copper.

According to the core construction and the manner in which the primary and secondary windings are placed around it, the transformer is named as the core type and shell type.

Core Type:

Core

The core of a transformer is constructed with a material having high permeability, such as silicon steel laminations in order to provide the continuous magnetic path; the core of the transformer is laminated for minimizing the eddy current loss.

The reason for using the steel core is that the core losses such as hysteresis losses and eddy current loss are reduced. Since the steel sheets have a very high resistivity, so the current losses are greatly reduced.

Core Type Construction of transformer:

In the core type construction of the transformer, rectangular frame laminations are formed to build the core of the transformer.  The primary and secondary windings are wound outside and surround the core ring. The windings are wound around the core in such a way that they surround the core ring on its outer edge.

In this type of construction, half of the winding is wrapped around each limb of the core and is enclosed in a manner such that no magnetic flux losses can occur and also the flux leakages can be minimized.

While placing these windings an insulation is provided between the core and low voltage winding (LV), between the two windings that are between LV and high voltage (HV) windings and also in between coils and yoke an also in between HV limb and To reduce the insulation, the low voltage winding is always placed nearer to the core.

core type electrical transformer construction
core type electrical transformer construction
core type electrical transformer construction
core type electrical transformer construction

 

The laminations are cut in the form of L-shape strips.

Shell type construction

In the shell type construction, both the windings (Primary winding and secondary winding) are wrapped around the same central limb.

In the shell type construction of the transformer, the windings pass through the inside of the core ring such that the core forms a shell outside the windings. This arrangement also prevents the flux leakages since both the windings are wrapped around the same central limb.

The primary winding and the secondary windings are placed on the central limb side by side. The low voltage winding is placed nearer to the core and the high voltage winding is placed outside the low voltage winding.

In the shell type transformer, the laminations are cut in the form of long strips of E shape and I shape. The central limb carries the whole of the flux whereas the side limbs carry half of the flux. Therefore, the width of the center is double to that of the outer limbs.

Dielectric Circuit

The dielectric circuit is used to insulate the conducting parts and the dielectric circuit consists of insulations used in different places in the transformer. The core of the transformer is laminated to minimize the eddy current losses. The laminations are insulated from each other by an oxide layer or by a light coating of varnish. The thickness of laminations varies from 0.35mm to 0.5mm for a frequency of 50 Hz.

Magnetic circuit

The magnetic circuit of a transformer provides the path to the flow of magnetic flux. The circuit consists of core and yoke. The limb is the vertical position on which the coil is wound and the horizontal position is known as the yoke. The core of the transformer is constructed in a manner to provide a continuous magnetic path by the use of the laminations of sheet steel or silicon steel assembled.

WINDINGS

An arrangement of windings is an important issue in the construction of the transformer. The Transformer consists of two windings namely Primary winding and secondary winding.

The winding connected to the main AC power supply is called the primary winding while the winding connected to the load or some external circuitry is called the secondary winding.

Windings of a transformer are made up of a conducting material. This allows the magnetic flux to build up and hence the current can be passed from one winding to another. Both the windings are wound on two separate limbs of iron to increase the magnetic flux. Iron is used because iron is an efficient conductor and exhibits excellent magnetic properties.

Since both the coils are wound on two separate limbs and due to the distance between them, flux leakages also occur which reduce the magnetic flux density and results in a reduced magnetic coupling between the two coil windings.

To avoid the above situation, the distance between the two windings is reduced, in order to minimize the flux leakages and a strong magnetic induction can be created and sustained between the two coils.

Other than these two main parts, a Transformer tank and Conservatory tank is also used in transformer construction:

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